1. Field of the Invention
This invention relates to torque converters and more particularly to torque converters with an associated clutch to control slip between the input and output components of a torque converter.
2. Description of the Related Art
Torque converters used in association with automatic transmissions for vehicles, under certain operating conditions, are subject to a substantial degree of slip resulting in reduced powertrain fuel efficiency.
One approach to the problem is to provide a lock-up clutch in association with the torque converter. Such lock-up clutches are shown in U.S. Pat. Nos. 3,497,043 and 4,305,487. While lock-up clutches solve the problem of excessive slip between the inlet and outlet components of a torque converter, they are subject to input distortions that require the addition of a spring damper assembly to attenuate torsional disturbances generated by an internal combustion engine connected to the input of the torque converter.
In the arrangement shown in the '043 patent, the damper assembly requires a spline ring connection to the turbine runner. Such arrangements are difficult to assemble and in the case of the '043 patent have only one friction surface in the clutch that in some cases may not provide enough friction surface area to lock-up torque converters having a high torque capacity.
In the arrangement shown in the '487 patent, the damper assembly includes a plate that is connected by weldments to the outer shell of the turbine runner. This connection is difficult to assemble. Furthermore, the '487 patent only shows a lock-up clutch that has one friction surface that in some cases may not provide enough friction surface to lock-up torque converters having a high torque capacity.
In still other prior art torque converter lock-up clutch designs, more than one friction surface is provided to increase the surface area of the friction surface in accordance with the torque capacity of the torque converter to assure lock-up.
In each of the aforedescribed arrangements, a spring damper assembly is provided to attenuate engine disturbances inputed to the torque converter.
An additional problem that occurs in the aforesaid clutch mechanisms is that, when subjected to alternate functional calibration scenarios, the operation of the clutch can cause increases in the local friction surface interface temperature elevating the automatic transmission fluid (ATF) operating temperature. Friction modifiers in such ATF degrade when temperatures increase so as to adversely affect the lock-up performance of the clutch.